Concrete Calculator
Cubic yards of ready-mix, or the number of 40, 60 and 80 lb bags, for slabs, footings and posts.
This concrete calculator takes the dimensions of what you are pouring and returns the volume in cubic yards for a ready-mix order, or the number of 40, 60 and 80 lb pre-mix bags if you are mixing on site.
For a poured floor or pad, the concrete slab calculator is set up for thickness in inches. For fence posts, use the post hole calculator, and for tube forms the Sonotube calculator.
Bags or ready-mix?
An 80 lb bag of pre-mix yields about 0.6 cubic feet, so it takes 45 bags to make one cubic yard. A 60 lb bag yields about 0.45 cubic feet — roughly 60 per yard. Below about half a cubic yard, bags are practical. Above it, bagged concrete costs far more per yard, takes much longer to place, and you risk cold joints between batches.
Ready-mix is sold by the cubic yard with a short-load fee under about one yard. Order to the nearest quarter yard and round up — you cannot add concrete to a pour that has started to set.
How much extra to order
Add 5 to 10% for a ready-mix order. Forms bulge, sub-grade is uneven, and spillage is normal. Running short on a slab pour means a visible cold joint or a second delivery fee. For bagged work, buy two or three spare bags — returning unopened bags is easier than a hardware-store run with wet concrete in the mixer.
Weight and delivery
Cured concrete weighs about 2 tons (4,000 lb) per cubic yard, so even a small slab is a heavy, permanent thing to place. A full mixer truck carries about 10 cubic yards. Confirm truck access and a wash-out area before the pour, and have enough hands to place and finish before it sets.
Common concrete-ordering mistakes
Mixing dozens of bags for a slab. Past about half a yard, hand-mixing means cold joints and an uneven finish — order ready-mix.
Ordering the exact calculated volume. Forms bulge and sub-grade is uneven; 5 to 10% extra avoids a cold joint or a second delivery.
Not checking truck access. A loaded mixer weighs 30+ tons and needs a wash-out spot — confirm both before the pour date.
Pouring on unprepared ground. Concrete needs 4 inches of compacted gravel base, not bare soil, or it cracks and settles.
| Product | Yield | Per cubic yard | Best for | Notes |
|---|---|---|---|---|
| Ready-mix (delivered) | 1 yd³ per yd³ | — | Slabs, driveways, footings > ½ yd³ | Short-load fee under ~1 yd³ |
| 80 lb bag | ~0.60 ft³ | 45 bags | Small pads, posts, repairs | ~4,000 psi mixed |
| 60 lb bag | ~0.45 ft³ | 60 bags | Post setting, small footings | Common fence-post size |
| 50 lb bag | ~0.375 ft³ | 72 bags | Small repairs | |
| 40 lb bag | ~0.30 ft³ | 90 bags | Patching, setting small posts | |
| Cured concrete weight | — | ~4,000 lb (2 tons) | — | 145–150 lb/ft³ |
Every material calculator
Each of these uses the same measured-drawing tool with the right density and bag sizes built in: gravel calculator , mulch calculator , concrete slab calculator , sand calculator , topsoil calculator , paver sand calculator , crushed stone calculator , sonotube concrete calculator , pea gravel calculator , river rock calculator , decomposed granite calculator , road base calculator . Or start from the material calculator homepage and pick a material there.
Frequently asked questions
How many 80 lb bags of concrete make a cubic yard?
About 45. An 80 lb bag yields roughly 0.6 cubic feet and a cubic yard is 27 cubic feet.
How many 60 lb bags of concrete make a cubic yard?
About 60. A 60 lb bag yields roughly 0.45 cubic feet.
How do I calculate concrete for a slab?
Multiply length × width × thickness, all in feet, then divide by 27 for cubic yards. A 10 ft × 10 ft slab at 4 inches (0.333 ft) thick is 33.3 cubic feet, about 1.23 cubic yards.
How much does a yard of concrete cost?
Ready-mix runs roughly $125 to $175 per cubic yard delivered in most of the US, plus short-load and delivery fees. Bagged concrete works out much higher per yard.
At what point should I switch from bags to ready-mix?
Around half a cubic yard. That is about 22 to 30 bags of mixing by hand — beyond that, ready-mix is cheaper, faster and gives a monolithic pour with no cold joints.
How much does a cubic yard of concrete weigh?
About 4,000 lb, or 2 tons, once cured. Wet concrete is slightly heavier.
How much concrete do I need for a fence post?
A 4-inch post in a 10-inch-wide hole 2 feet deep needs about 0.75 cubic feet — roughly one and a half 60 lb bags. Use the post hole calculator for other sizes.
Should I order extra concrete?
Yes — 5 to 10% for ready-mix to cover uneven sub-grade and form bulge, or two to three spare bags for small jobs.
How much does a truckload of concrete cover?
A full mixer carries about 10 cubic yards — enough for a 4-inch slab of roughly 800 square feet, or about 40 feet of 12-inch-wide footing at 2 feet deep.
How long do I have to place concrete after it is delivered?
Usually 60 to 90 minutes from batching in mild weather, less when it is hot. Have enough hands and tools ready before the truck arrives.
Can I pour concrete in cold weather?
Above 40°F is workable with care; below that you need heated water, accelerator, blankets and protection from freezing for the first 24 to 48 hours.
How much rebar do I need in a slab?
A residential slab typically uses #3 or #4 bar on an 18-inch grid, or 6×6 W1.4 welded wire mesh, kept in the middle third of the slab thickness on chairs.
What is the short-load fee?
Ready-mix plants charge a fee — often $50 to $150 — for orders under about 1 cubic yard, because a partial load still ties up a truck.